全文获取类型
收费全文 | 2687篇 |
免费 | 2篇 |
国内免费 | 19篇 |
专业分类
航空 | 1321篇 |
航天技术 | 1067篇 |
综合类 | 10篇 |
航天 | 310篇 |
出版年
2019年 | 19篇 |
2018年 | 24篇 |
2017年 | 18篇 |
2016年 | 17篇 |
2014年 | 49篇 |
2013年 | 59篇 |
2012年 | 54篇 |
2011年 | 83篇 |
2010年 | 62篇 |
2009年 | 105篇 |
2008年 | 157篇 |
2007年 | 63篇 |
2006年 | 67篇 |
2005年 | 70篇 |
2004年 | 80篇 |
2003年 | 82篇 |
2002年 | 51篇 |
2001年 | 75篇 |
2000年 | 49篇 |
1999年 | 64篇 |
1998年 | 81篇 |
1997年 | 51篇 |
1996年 | 61篇 |
1995年 | 78篇 |
1994年 | 76篇 |
1993年 | 50篇 |
1992年 | 61篇 |
1991年 | 31篇 |
1990年 | 30篇 |
1989年 | 70篇 |
1988年 | 26篇 |
1987年 | 28篇 |
1986年 | 30篇 |
1985年 | 121篇 |
1984年 | 68篇 |
1983年 | 57篇 |
1982年 | 58篇 |
1981年 | 103篇 |
1980年 | 34篇 |
1979年 | 27篇 |
1978年 | 24篇 |
1977年 | 28篇 |
1976年 | 18篇 |
1975年 | 31篇 |
1974年 | 19篇 |
1973年 | 25篇 |
1972年 | 20篇 |
1971年 | 16篇 |
1970年 | 24篇 |
1969年 | 26篇 |
排序方式: 共有2708条查询结果,搜索用时 15 毫秒
991.
A low-dimensional test problem with a known solution is used to verify various computer implementations of F.C. Schweppe's likelihood detector (1965). In this case a closed-form solution is provided for a Schweppe likelihood detector in terms of an intermediate Kalman filter, as utilized in its implementation, for detecting the presence of a two-state signal model in Gaussian white noise. The associated error probabilities are also evaluated following a procedure that utilizes optimized Chernoff-like bounds for a tight approximation. A methodology is demonstrated for appropriately setting the decision threshold for this example as a tradeoff against allowable observation time. By using this or similar examples, certain qualitative and quantitative aspects of the software implementation can be checked for conformance to anticipated behavior as an intermediate benchmark, prior to modular replacement of the various high-order matrices appropriate to the particular application 相似文献
992.
H Rahmann R H Anken 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2002,30(4):697-710
During the entire evolution of life on Earth, the development of all organisms took place under constant gravity conditions, against which they achieved specific countermeasures for compensation and adaptation. On this background, it is still an open question to which extent altered gravity such as hypergravity (centrifuge) or microgravity (spaceflight) affects the normal individual development, either on the systemic level of the whole organism or on the level of individual organs or even single cells. The present review provides information on these questions, comprising gravistimulated effects on invertebrates and vertebrates (with the exception of mammals, since respective biomedically oriented reviews abound), focusing on developing fish as model systems, with special emphasis on the effect of altered gravity on the developing brain and vestibular system, comprising investigations on behaviour and plastic reactivities of the brain and inner ear. Clues and insights into the possible basic causes of space motion sickness-phenomena (SMS; a kinetosis) are provided as well as perspectives in regard to future work to be done including studies on the ISS concerning the analysis of gravistimulated effects on developmental issues (imprinting phase for graviperception?). 相似文献
993.
H. Tanabe S. Isobe H. Akiyama Y. Koma T. Okabe J. Nishimura T. Maihara K. Mizutani J. Soegijo T.E. Hariadi S. Indrawan S. Slamet P. Anondo T. Tatang S. Agus W. Mulyana V.R. Suroto 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1985,5(1):69-72
A balloon observation of the total solar eclipse on 11 June 1983 was carried out as a cooperative work between Japanese and Indonesian teams. The observation was a photo-polarimetry of the F corona in both visual and near-infrared regions.The balloon of 15,000-m3 with a payload of 150-kg was launched at 7h13m on 11 June from Watukosek Balloon Base in East Java. Observation at an altitude of 30.5-km was successfully made during the totality (11h28~32m) at a position of ~40-km east-south-east from Jogjakarta.As a preliminary result, an excess in infrared brightness has been found near the position of 3.8R⊙ west from the sun, which may be due to thermal emission from a high-temperature dust cloud located around the sun. 相似文献
994.
H. Okuda 《Space Science Reviews》1985,42(1-2):41-52
Several numerical plasma simulation models using particles are described which are appropriate for low frequency electrostatic
and electromagnetic microinstabilities in a strong magnetic field. The model makes use of the guiding center drift approximations
for the electrons while the ions are represented either as particles obeying the equation of motion with the full Lorentz
force or a fluid which includes finite-Larmor-radius effects. These models are particularly useful for studying low frequency
microinstabilities (ω ≲ ωpi, Ωi) propagating nearly perpendicular to an external magnetic field (k⊥ ≫ k∥). 相似文献
995.
F. Verbunt G. Hasinger H. M. Johnston W. Bunk 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1993,13(12):151-160
We review the first observations of globular clusters obtained with the X-ray telescope on board of the ROSAT satellite. In the All-Sky Survey, all known bright sources and two new transient sources were detected. In addition a super-soft source was found in NGC5272. Concerning the dim sources, the survey suggests that those outside the core of ω Cen are not related to the cluster. The survey further improved by one or two magnitudes on many upper limits previously obtained by the HEAO-1 satellite. Pointed observations have improved the positional accuracy of a number of sources, and added to the number of known dim sources. In 47 Tuc, the known central source is resolved into 4 separate sources, which we argue are all soft X-ray transients. A comparison with observations of the old open cluster M67 leads us to suggest that some of the dim sources may be conglomerates of a large number of RS Can Ven type binaries. 相似文献
996.
H E Rauch D B Schaechter 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1994,14(11):297-305
Advances in the theory and technology of artificial neural networks provide the potential for new approaches to the problems of control, identification, and diagnosis for large, complex systems. However, these approaches must be validated for specific applications before they can be exploited effectively. Because of the unique capabilities they offer, neural networks should play an important role in space exploration systems operations. After a brief introduction to neural networks is presented, some applications of neural networks to identification and control of space systems are described and discussed. They span the spectrum of relatively straightforward to rather complex applications. An explanation of how neural networks can be applied to such important tasks as fault diagnosis and accommodation is presented. Neural networks are shown to be part of the hierarchy of intelligent control where a higher order decision element monitors and supervises lower order elements for sensing and actuation. 相似文献
997.
R. Grabowski B. Bösch H. Wolf 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1982,2(7):169-172
Signals obtained on board rocket payloads or satellites are often “spin modulated”. The relevant information is then found within the envelope and the phase of the signal. The most efficient method of extracting this information is the numerical Fourier analysis. 相似文献
998.
The capability of lead-acid batteries for supplying very high power for a short time is explored. The application of such a battery for accelerating a hypersonic plane is used to illustrate the requirements. A technique for analyzing batteries and controlling voltage for pulse loads is described. Evaluation of lead-acid batteries in production and voltage regulation by switching batteries in and out are covered. Alternatives to batteries, including superconducting magnetic energy storage, are discussed 相似文献
999.
J.G. Luhmann R.C. Elphic C.T. Russell L.H. Brace R.E. Hartle 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1982,2(10):17-21
Theoretical models of the ionosphere of Venus have been constructed in the past without due consideration of the fact that the ionosphere is sometimes magnetized. This paper examines some differences between the magnetized and unmagnetized dayside Venus ionosphere using the Pioneer Venus Orbiter Langmuir probe and magnetometer data. Particular attention is given to the evaluation of the altitude profiles of the thermal electron heating and comparison of the magnitude of the magnetic force(¯vׯB) ׯB with other forces in the ionosphere. Several examples illustrate how heating profiles are different in the magnetized ionosphere with effective heating below ~200 km altitude reduced by orders of magnitude compared to the field-free ionosphere. The force associated with the magnetic field is comparable to other forces in the magnetized ionosphere. The measured plasma density, electron temperature and magnetic field thus suggest that large-scale magnetic fields should be included in future ionosphere models. 相似文献
1000.
H D Pross M Kost J Kiefer 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1994,14(10):125-130
The influence of microgravity on the repair of radiation induced genetic damage in a temperature-conditional repair mutant of the yeast Saccharomyces cerevisiae (rad 54-3) was investigated onboard the IML-1 mission (January 22nd-30th 1992, STS-42). Cells were irradiated before the flight, incubated under microgravity at the permissive (22 degrees C) and restrictive (36 degrees C) temperature and afterwards tested for survival. The results suggest that repair may be reduced under microgravity. 相似文献